Ask the Doctor: This Cyst on My Foot is Killing Me!

Q: I recently developed an excruciating pain on the bottom of my foot. One day, I felt fine with no tenderness at all and the next I was unable to put any weight on it without searing pain. There is a cyst-like lump under the skin on the bottom of my foot. My doctor believes that it is a plantar fibroma. I researched plantar fibroma and everything I read talked about the cysts recurring and possibly needing to remove the plantar fascia. Now I am afraid that my competitive running days may be over. Can you tell me anything encouraging about this diagnosis?

-- Kathy, Massachusettes

A: A plantar fibroma is a benign lump that typically develops gradually. It does not tend to be especially painful, though weightbearing on the lump may be uncomfortable. If this is a superficial fibroma it may spontaneously resolve over time.

The sudden onset of severe pain is not typical for a fibroma. A rupture/ partial rupture of the plantar fascia is extremely painful, though the lump that may develop due to scar tissue usually develops weeks following the injury. A cyst could develop fairly quickly and due to distention, it could be very painful. A foreign body could cause a painful lump under the skin. Scar tissue around a nerve in the foot (neuroma) could present as a very painful lump.

Since your history is not typical of a fibroma, further evaluation with MRI or ultrasound would provide more details regarding the mass. This will help determine the best course of treatment.

Padding around the lump when weight-bearing may help diminish pain. If the lump is a cyst, it could be drained. A cortisone injection could also be helpful.

Surgical excision is the last option if a painful lump persists despite these measures. Lumps and cysts can recur following surgical excision, but this does not necessarily require extensive repeat surgery. Find out what the lump is so the appropriate treatment may be initiated.Related : Metatarsalgia